use chrono::{Datelike, Months, NaiveDate};
use encoding_rs::{UTF_8, WINDOWS_1252, ISO_8859_15};
use serde::Serialize;
use sha2::{Digest, Sha256};
use std::fs;
use std::path::Path;
use tauri_plugin_dialog::DialogExt;
use walkdir::WalkDir;

#[derive(Debug, Serialize, Clone)]
pub struct ScannedFile {
    pub filename: String,
    pub file_path: String,
    pub size_bytes: u64,
    pub modified_at: String,
}

#[derive(Debug, Serialize, Clone)]
pub struct ScannedSource {
    pub folder_name: String,
    pub folder_path: String,
    pub files: Vec<ScannedFile>,
}

#[tauri::command]
pub fn scan_import_folder(folder_path: String) -> Result<Vec<ScannedSource>, String> {
    let root = Path::new(&folder_path);
    if !root.is_dir() {
        return Err(format!("Folder does not exist: {}", folder_path));
    }

    let mut sources: Vec<ScannedSource> = Vec::new();

    let entries = fs::read_dir(root).map_err(|e| format!("Cannot read folder: {}", e))?;

    for entry in entries {
        let entry = entry.map_err(|e| format!("Error reading entry: {}", e))?;
        let path = entry.path();

        if !path.is_dir() {
            continue;
        }

        let folder_name = path
            .file_name()
            .unwrap_or_default()
            .to_string_lossy()
            .to_string();

        // Skip hidden folders
        if folder_name.starts_with('.') {
            continue;
        }

        let mut files: Vec<ScannedFile> = Vec::new();

        for file_entry in WalkDir::new(&path).max_depth(1).into_iter().flatten() {
            let file_path = file_entry.path();
            if !file_path.is_file() {
                continue;
            }

            let ext = file_path
                .extension()
                .unwrap_or_default()
                .to_string_lossy()
                .to_lowercase();

            if ext != "csv" && ext != "txt" {
                continue;
            }

            let metadata = fs::metadata(file_path)
                .map_err(|e| format!("Cannot read metadata: {}", e))?;

            let modified_at = metadata
                .modified()
                .map(|t| {
                    let duration = t
                        .duration_since(std::time::UNIX_EPOCH)
                        .unwrap_or_default();
                    duration.as_secs().to_string()
                })
                .unwrap_or_default();

            files.push(ScannedFile {
                filename: file_path
                    .file_name()
                    .unwrap_or_default()
                    .to_string_lossy()
                    .to_string(),
                file_path: file_path.to_string_lossy().to_string(),
                size_bytes: metadata.len(),
                modified_at,
            });
        }

        files.sort_by(|a, b| a.filename.cmp(&b.filename));

        sources.push(ScannedSource {
            folder_name,
            folder_path: path.to_string_lossy().to_string(),
            files,
        });
    }

    sources.sort_by(|a, b| a.folder_name.cmp(&b.folder_name));

    Ok(sources)
}

#[tauri::command]
pub fn read_file_content(file_path: String, encoding: String) -> Result<String, String> {
    let bytes = fs::read(&file_path).map_err(|e| format!("Cannot read file: {}", e))?;

    let content = decode_bytes(&bytes, &encoding)?;
    Ok(content)
}

#[tauri::command]
pub fn hash_file(file_path: String) -> Result<String, String> {
    let bytes = fs::read(&file_path).map_err(|e| format!("Cannot read file: {}", e))?;
    let mut hasher = Sha256::new();
    hasher.update(&bytes);
    let result = hasher.finalize();
    Ok(format!("{:x}", result))
}

#[tauri::command]
pub fn detect_encoding(file_path: String) -> Result<String, String> {
    let bytes = fs::read(&file_path).map_err(|e| format!("Cannot read file: {}", e))?;

    // Check BOM
    if bytes.starts_with(&[0xEF, 0xBB, 0xBF]) {
        return Ok("utf-8".to_string());
    }
    if bytes.starts_with(&[0xFF, 0xFE]) {
        return Ok("utf-16le".to_string());
    }
    if bytes.starts_with(&[0xFE, 0xFF]) {
        return Ok("utf-16be".to_string());
    }

    // Try UTF-8 first
    if std::str::from_utf8(&bytes).is_ok() {
        return Ok("utf-8".to_string());
    }

    // Default to windows-1252 for French bank CSVs
    Ok("windows-1252".to_string())
}

#[tauri::command]
pub fn get_file_preview(
    file_path: String,
    encoding: String,
    max_lines: usize,
) -> Result<String, String> {
    let bytes = fs::read(&file_path).map_err(|e| format!("Cannot read file: {}", e))?;
    let content = decode_bytes(&bytes, &encoding)?;

    let lines: Vec<&str> = content.lines().take(max_lines).collect();
    Ok(lines.join("\n"))
}

#[tauri::command]
pub async fn pick_folder(app: tauri::AppHandle) -> Result<Option<String>, String> {
    let folder = app
        .dialog()
        .file()
        .blocking_pick_folder();

    Ok(folder.map(|f| f.to_string()))
}

/// Folder names the onboarding samples are written under — the same in FR and
/// EN (decided in planning), so the scan shows one source per bank whatever the
/// UI language.
const SAMPLE_DESJARDINS_FOLDER: &str = "Exemple Desjardins";
const SAMPLE_TANGERINE_FOLDER: &str = "Exemple Tangerine";

/// Sample statements embedded at compile time. The paths are relative to
/// `src-tauri/src/commands/`; the same files are read by vitest, so the Rust
/// command and the detection test cannot drift apart.
const SAMPLE_DESJARDINS_TEMPLATE: &str =
    include_str!("../../../src/__fixtures__/samples/exemple-desjardins.csv");
const SAMPLE_TANGERINE_TEMPLATE: &str =
    include_str!("../../../src/__fixtures__/samples/exemple-tangerine.csv");

/// Write the two onboarding sample statements (a Desjardins chequing account and
/// a Tangerine credit card, both synthetic) into `import_folder`, one sub-folder
/// each, so that the very next scan of the import folder shows two sources a
/// new user can import right away.
///
/// `today` is the webview's local date as `YYYY-MM-DD`; chrono is compiled
/// without `clock`, so the command never reads the system clock and stays
/// deterministic. The templates carry `{{M1}}` / `{{M2}}` tokens, rendered as
/// `MM/YYYY` of the two complete months before `today` (`{{M1}}` the most
/// recent), and each file is named `releve-YYYY-MM.csv` after `{{M1}}`.
///
/// Refuses to run when `import_folder` is not a directory, and when either
/// sample folder already exists — checked BEFORE anything is written, so an
/// existing folder is never touched. The command only ever receives the import
/// folder and a date: the names of what it writes are fixed here. Returns the
/// two folder NAMES (not paths).
#[tauri::command]
pub fn create_sample_import_folders(
    import_folder: String,
    today: String,
) -> Result<Vec<String>, String> {
    let today = NaiveDate::parse_from_str(&today, "%Y-%m-%d")
        .map_err(|e| format!("Invalid date '{}': {}", today, e))?;
    let first_of_month = today
        .with_day(1)
        .ok_or_else(|| "Cannot compute the first day of the month".to_string())?;
    let m1 = first_of_month
        .checked_sub_months(Months::new(1))
        .ok_or_else(|| "Cannot compute the previous month".to_string())?;
    let m2 = first_of_month
        .checked_sub_months(Months::new(2))
        .ok_or_else(|| "Cannot compute the month before the previous one".to_string())?;

    let root = Path::new(&import_folder);
    if !root.is_dir() {
        return Err(format!("Folder does not exist: {}", import_folder));
    }

    let samples: [(&str, &str); 2] = [
        (SAMPLE_DESJARDINS_FOLDER, SAMPLE_DESJARDINS_TEMPLATE),
        (SAMPLE_TANGERINE_FOLDER, SAMPLE_TANGERINE_TEMPLATE),
    ];

    // Both existence checks run before the first write: a user who already has
    // one of the folders keeps it untouched and gets neither.
    for (folder_name, _) in &samples {
        if root.join(folder_name).exists() {
            return Err(format!("Folder already exists: {}", folder_name));
        }
    }

    let m1_token = m1.format("%m/%Y").to_string();
    let m2_token = m2.format("%m/%Y").to_string();
    let filename = format!("releve-{}.csv", m1.format("%Y-%m"));

    let mut created: Vec<String> = Vec::with_capacity(samples.len());
    for (folder_name, template) in &samples {
        let folder = root.join(folder_name);
        fs::create_dir(&folder)
            .map_err(|e| format!("Cannot create folder {}: {}", folder_name, e))?;
        let content = template
            .replace("{{M1}}", &m1_token)
            .replace("{{M2}}", &m2_token);
        fs::write(folder.join(&filename), content)
            .map_err(|e| format!("Cannot write {}/{}: {}", folder_name, filename, e))?;
        created.push((*folder_name).to_string());
    }

    Ok(created)
}

fn decode_bytes(bytes: &[u8], encoding: &str) -> Result<String, String> {
    // Strip BOM if present
    let bytes = if bytes.starts_with(&[0xEF, 0xBB, 0xBF]) {
        &bytes[3..]
    } else {
        bytes
    };

    match encoding.to_lowercase().as_str() {
        "utf-8" | "utf8" => {
            String::from_utf8(bytes.to_vec()).map_err(|e| format!("UTF-8 decode error: {}", e))
        }
        "windows-1252" | "cp1252" => {
            let (cow, _, had_errors) = WINDOWS_1252.decode(bytes);
            if had_errors {
                Err("Windows-1252 decode error".to_string())
            } else {
                Ok(cow.into_owned())
            }
        }
        "iso-8859-1" | "iso-8859-15" | "latin1" | "latin9" => {
            let (cow, _, had_errors) = ISO_8859_15.decode(bytes);
            if had_errors {
                Err("ISO-8859-15 decode error".to_string())
            } else {
                Ok(cow.into_owned())
            }
        }
        _ => {
            // Fallback to UTF-8
            let (cow, _, _) = UTF_8.decode(bytes);
            Ok(cow.into_owned())
        }
    }
}

#[cfg(test)]
mod sample_folder_tests {
    use super::*;
    use std::path::PathBuf;

    /// One scratch directory per CASE: the cases of this binary run in parallel
    /// inside a single process, so `process::id()` alone would make them share
    /// — and trip over — the same folder.
    fn sandbox(name: &str) -> PathBuf {
        let dir = std::env::temp_dir().join(format!(
            "simpl-resultat-samples-{}-{}",
            std::process::id(),
            name
        ));
        let _ = fs::remove_dir_all(&dir);
        fs::create_dir_all(&dir).expect("sandbox created");
        dir
    }

    fn cleanup(dir: &Path) {
        let _ = fs::remove_dir_all(dir);
    }

    fn as_arg(path: &Path) -> String {
        path.to_string_lossy().to_string()
    }

    /// Every `DD/MM/YYYY` date of a rendered file must fall in one of the two
    /// expected months — no token left, no third month.
    fn assert_dates_in(content: &str, months: &[&str]) {
        assert!(!content.contains("{{"), "token left in {}", content);
        for line in content.lines().skip(1) {
            let date = line.split([';', ',']).next().unwrap();
            assert_eq!(date.len(), 10, "unexpected date {}", date);
            let month_year = &date[3..];
            assert!(
                months.contains(&month_year),
                "date {} is outside {:?}",
                date,
                months
            );
        }
    }

    #[test]
    fn refuses_a_missing_import_folder() {
        let dir = sandbox("missing");
        let missing = dir.join("nope");
        let result = create_sample_import_folders(as_arg(&missing), "2026-09-25".to_string());
        cleanup(&dir);
        let err = result.unwrap_err();
        assert!(err.contains("does not exist"), "{}", err);
    }

    #[test]
    fn refuses_when_desjardins_folder_exists_and_writes_nothing() {
        let dir = sandbox("existing");
        fs::create_dir(dir.join(SAMPLE_DESJARDINS_FOLDER)).unwrap();
        let result = create_sample_import_folders(as_arg(&dir), "2026-09-25".to_string());
        let tangerine_created = dir.join(SAMPLE_TANGERINE_FOLDER).exists();
        let desjardins_empty = fs::read_dir(dir.join(SAMPLE_DESJARDINS_FOLDER))
            .unwrap()
            .next()
            .is_none();
        cleanup(&dir);
        let err = result.unwrap_err();
        assert!(err.contains(SAMPLE_DESJARDINS_FOLDER), "{}", err);
        assert!(!tangerine_created, "Exemple Tangerine must not be created");
        assert!(desjardins_empty, "the existing folder must stay untouched");
    }

    #[test]
    fn writes_both_folders_for_the_two_previous_months() {
        let dir = sandbox("success");
        let result = create_sample_import_folders(as_arg(&dir), "2026-09-25".to_string());
        let read = |folder: &str| {
            fs::read_to_string(dir.join(folder).join("releve-2026-08.csv"))
        };
        let desjardins = read(SAMPLE_DESJARDINS_FOLDER);
        let tangerine = read(SAMPLE_TANGERINE_FOLDER);
        let desjardins_count = fs::read_dir(dir.join(SAMPLE_DESJARDINS_FOLDER)).unwrap().count();
        let tangerine_count = fs::read_dir(dir.join(SAMPLE_TANGERINE_FOLDER)).unwrap().count();
        cleanup(&dir);

        assert_eq!(
            result.unwrap(),
            vec![
                SAMPLE_DESJARDINS_FOLDER.to_string(),
                SAMPLE_TANGERINE_FOLDER.to_string()
            ]
        );
        let desjardins = desjardins.expect("Desjardins file written");
        let tangerine = tangerine.expect("Tangerine file written");
        assert_eq!(desjardins_count, 1);
        assert_eq!(tangerine_count, 1);
        assert_eq!(desjardins.lines().count(), 41);
        assert_eq!(tangerine.lines().count(), 41);
        assert_dates_in(&desjardins, &["08/2026", "07/2026"]);
        assert_dates_in(&tangerine, &["08/2026", "07/2026"]);
        assert!(desjardins.contains("08/2026") && desjardins.contains("07/2026"));
        assert!(tangerine.contains("08/2026") && tangerine.contains("07/2026"));
    }

    #[test]
    fn refuses_an_unparseable_date_before_writing() {
        let dir = sandbox("bad-date");
        let result = create_sample_import_folders(as_arg(&dir), "pas-une-date".to_string());
        let anything_written = fs::read_dir(&dir).unwrap().next().is_some();
        cleanup(&dir);
        let err = result.unwrap_err();
        assert!(err.contains("Invalid date"), "{}", err);
        assert!(!anything_written);
    }

    #[test]
    fn crosses_the_year_boundary() {
        let dir = sandbox("year-boundary");
        let result = create_sample_import_folders(as_arg(&dir), "2027-01-15".to_string());
        let desjardins =
            fs::read_to_string(dir.join(SAMPLE_DESJARDINS_FOLDER).join("releve-2026-12.csv"));
        let tangerine =
            fs::read_to_string(dir.join(SAMPLE_TANGERINE_FOLDER).join("releve-2026-12.csv"));
        cleanup(&dir);

        assert!(result.is_ok());
        let desjardins = desjardins.expect("Desjardins file named after December");
        let tangerine = tangerine.expect("Tangerine file named after December");
        assert_dates_in(&desjardins, &["12/2026", "11/2026"]);
        assert_dates_in(&tangerine, &["12/2026", "11/2026"]);
        assert!(desjardins.contains("12/2026") && desjardins.contains("11/2026"));
        assert!(tangerine.contains("12/2026") && tangerine.contains("11/2026"));
    }
}