use std::path::PathBuf;

use codex_utils_absolute_path::AbsolutePathBuf;

use crate::shell_detect::ShellType;
use crate::shell_detect::detect_shell_type;

const POWERSHELL_FLAGS: &[&str] = &["-nologo", "-noprofile", "-command", "-c"];

/// Prefixed command for powershell shell calls to force UTF-8 console output.
pub const UTF8_OUTPUT_PREFIX: &str = "[Console]::OutputEncoding=[System.Text.Encoding]::UTF8;\n";

pub fn prefix_powershell_script_with_utf8(command: &[String]) -> Vec<String> {
    let Some((_, script)) = extract_powershell_command(command) else {
        return command.to_vec();
    };

    let trimmed = script.trim_start();
    let script = if trimmed.starts_with(UTF8_OUTPUT_PREFIX) {
        script.to_string()
    } else {
        format!("{UTF8_OUTPUT_PREFIX}{script}")
    };

    let mut command: Vec<String> = command[..(command.len() - 1)]
        .iter()
        .map(std::string::ToString::to_string)
        .collect();
    command.push(script);
    command
}

/// Extract the PowerShell script body from an invocation such as:
///
/// - ["pwsh", "-NoProfile", "-Command", "Get-ChildItem -Recurse | Select-String foo"]
/// - ["powershell.exe", "-Command", "Write-Host hi"]
/// - ["powershell", "-NoLogo", "-NoProfile", "-Command", "...script..."]
///
/// Returns (`shell`, `script`) when the first arg is a PowerShell executable and a
/// `-Command` (or `-c`) flag is present followed by a script string.
pub fn extract_powershell_command(command: &[String]) -> Option<(&str, &str)> {
    if command.len() < 3 {
        return None;
    }

    let shell = &command[0];
    if !matches!(
        detect_shell_type(&PathBuf::from(shell)),
        Some(ShellType::PowerShell)
    ) {
        return None;
    }

    // Find the first occurrence of -Command (accept common short alias -c as well)
    let mut i = 1usize;
    while i + 1 < command.len() {
        let flag = &command[i];
        // Reject unknown flags
        if !POWERSHELL_FLAGS.contains(&flag.to_ascii_lowercase().as_str()) {
            return None;
        }
        if flag.eq_ignore_ascii_case("-Command") || flag.eq_ignore_ascii_case("-c") {
            let script = &command[i + 1];
            return Some((shell, script));
        }
        i += 1;
    }
    None
}

/// This function attempts to find a valid PowerShell executable on the system.
/// It first tries to find pwsh.exe, and if that fails, it tries to find
/// powershell.exe.
#[cfg(windows)]
#[allow(dead_code)]
pub(crate) fn try_find_powershellish_executable_blocking() -> Option<AbsolutePathBuf> {
    if let Some(pwsh_path) = try_find_pwsh_executable_blocking() {
        Some(pwsh_path)
    } else {
        try_find_powershell_executable_blocking()
    }
}

/// This function attempts to find a powershell.exe executable on the system.
pub fn try_find_powershell_executable_blocking() -> Option<AbsolutePathBuf> {
    try_find_powershellish_executable_in_path(&["powershell.exe"])
}

/// This function attempts to find a pwsh.exe executable on the system.
/// Note that pwsh.exe and powershell.exe are different executables:
///
/// - pwsh.exe is the cross-platform PowerShell Core (v6+) executable
/// - powershell.exe is the Windows PowerShell (v5.1 and earlier) executable
///
/// Further, while powershell.exe is included by default on Windows systems,
/// pwsh.exe must be installed separately by the user. And even when the user
/// has installed pwsh.exe, it may not be available in the system PATH, in which
/// case we attempt to locate it via other means.
pub fn try_find_pwsh_executable_blocking() -> Option<AbsolutePathBuf> {
    if let Some(ps_home) = std::process::Command::new("cmd")
        .args(["/C", "pwsh", "-NoProfile", "-Command", "$PSHOME"])
        .output()
        .ok()
        .and_then(|out| {
            if !out.status.success() {
                return None;
            }
            let stdout = String::from_utf8_lossy(&out.stdout);
            let trimmed = stdout.trim();
            (!trimmed.is_empty()).then(|| trimmed.to_string())
        })
    {
        let candidate = AbsolutePathBuf::resolve_path_against_base("pwsh.exe", &ps_home);

        if let Ok(candidate_abs_path) = candidate
            && is_powershellish_executable_available(candidate_abs_path.as_path())
        {
            return Some(candidate_abs_path);
        }
    }

    try_find_powershellish_executable_in_path(&["pwsh.exe"])
}

fn try_find_powershellish_executable_in_path(candidates: &[&str]) -> Option<AbsolutePathBuf> {
    for candidate in candidates {
        let Ok(resolved_path) = which::which(candidate) else {
            continue;
        };

        if !is_powershellish_executable_available(&resolved_path) {
            continue;
        }

        let Ok(abs_path) = AbsolutePathBuf::from_absolute_path(resolved_path) else {
            continue;
        };

        return Some(abs_path);
    }

    None
}

fn is_powershellish_executable_available(powershell_or_pwsh_exe: &std::path::Path) -> bool {
    // This test works for both powershell.exe and pwsh.exe.
    std::process::Command::new(powershell_or_pwsh_exe)
        .args(["-NoLogo", "-NoProfile", "-Command", "Write-Output ok"])
        .output()
        .map(|output| output.status.success())
        .unwrap_or(false)
}

#[cfg(test)]
mod tests {
    use super::extract_powershell_command;

    #[test]
    fn extracts_basic_powershell_command() {
        let cmd = vec![
            "powershell".to_string(),
            "-Command".to_string(),
            "Write-Host hi".to_string(),
        ];
        let (_shell, script) = extract_powershell_command(&cmd).expect("extract");
        assert_eq!(script, "Write-Host hi");
    }

    #[test]
    fn extracts_lowercase_flags() {
        let cmd = vec![
            "powershell".to_string(),
            "-nologo".to_string(),
            "-command".to_string(),
            "Write-Host hi".to_string(),
        ];
        let (_shell, script) = extract_powershell_command(&cmd).expect("extract");
        assert_eq!(script, "Write-Host hi");
    }

    #[test]
    fn extracts_full_path_powershell_command() {
        let command = if cfg!(windows) {
            "C:\\windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe".to_string()
        } else {
            "/usr/local/bin/powershell.exe".to_string()
        };
        let cmd = vec![command, "-Command".to_string(), "Write-Host hi".to_string()];
        let (_shell, script) = extract_powershell_command(&cmd).expect("extract");
        assert_eq!(script, "Write-Host hi");
    }

    #[test]
    fn extracts_with_noprofile_and_alias() {
        let cmd = vec![
            "pwsh".to_string(),
            "-NoProfile".to_string(),
            "-c".to_string(),
            "Get-ChildItem | Select-String foo".to_string(),
        ];
        let (_shell, script) = extract_powershell_command(&cmd).expect("extract");
        assert_eq!(script, "Get-ChildItem | Select-String foo");
    }
}