use crate::{system_info, InstallError};

/// Apply registry entries using native Windows registry APIs.
///
/// The entries are in .reg file format (without the header line).
/// Supported syntax:
/// - `[HKEY_xxx\path]` — create/open key
/// - `[-HKEY_xxx\path]` — delete entire key tree
/// - `"name"="string_value"` — set REG_SZ value
/// - `"name"=dword:XXXXXXXX` — set REG_DWORD value
/// - `"name"=-` — delete a value
/// - `@="string_value"` — set the default (unnamed) value
#[cfg(windows)]
pub fn apply_registry(entries: &[&str]) -> Result<(), InstallError> {
    let combined = entries.join("\n\n");
    let filled = system_info::fill_string(&combined);
    apply_reg_content(&filled)
}

#[cfg(windows)]
fn apply_reg_content(content: &str) -> Result<(), InstallError> {
    use windows_sys::Win32::System::Registry::{
        RegCloseKey, RegCreateKeyExW, RegDeleteValueW, RegSetValueExW,
        KEY_WOW64_64KEY, KEY_WRITE, REG_DWORD, REG_OPTION_NON_VOLATILE, REG_SZ,
    };

    let mut current_hkey: Option<windows_sys::Win32::System::Registry::HKEY> = None;

    for line in content.lines() {
        let line = line.trim();
        if line.is_empty() {
            continue;
        }

        // Delete key: [-HKEY_xxx\path]
        if line.starts_with("[-") && line.ends_with(']') {
            if let Some(hk) = current_hkey.take() {
                unsafe { RegCloseKey(hk) };
            }

            let key_path = &line[2..line.len() - 1];
            if let Some((root, subkey)) = parse_root_and_subkey(key_path) {
                delete_key_tree(root, subkey);
            }
            continue;
        }

        // Open/create key: [HKEY_xxx\path]
        if line.starts_with('[') && line.ends_with(']') {
            if let Some(hk) = current_hkey.take() {
                unsafe { RegCloseKey(hk) };
            }

            let key_path = &line[1..line.len() - 1];
            if let Some((root, subkey)) = parse_root_and_subkey(key_path) {
                let subkey_wide: Vec<u16> =
                    subkey.encode_utf16().chain(std::iter::once(0)).collect();
                unsafe {
                    let mut hkey = std::ptr::null_mut();
                    let mut disposition: u32 = 0;
                    let result = RegCreateKeyExW(
                        root,
                        subkey_wide.as_ptr(),
                        0,
                        std::ptr::null(),
                        REG_OPTION_NON_VOLATILE,
                        KEY_WRITE | KEY_WOW64_64KEY,
                        std::ptr::null(),
                        &mut hkey,
                        &mut disposition,
                    );
                    if result == 0 {
                        current_hkey = Some(hkey);
                    }
                }
            }
            continue;
        }

        // Value operations require an open key.
        let Some(hkey) = current_hkey else {
            continue;
        };

        // Default value: @="value"
        if let Some(rest) = line.strip_prefix("@=") {
            if let Some(val) = parse_reg_string(rest) {
                let val_wide: Vec<u16> =
                    val.encode_utf16().chain(std::iter::once(0)).collect();
                unsafe {
                    RegSetValueExW(
                        hkey,
                        std::ptr::null(),
                        0,
                        REG_SZ as u32,
                        val_wide.as_ptr() as *const u8,
                        (val_wide.len() * 2) as u32,
                    );
                }
            }
            continue;
        }

        // Named value: "name"=...
        if !line.starts_with('"') {
            continue;
        }

        let Some((name, value_part)) = parse_name_and_value(line) else {
            continue;
        };

        let name_wide: Vec<u16> = name.encode_utf16().chain(std::iter::once(0)).collect();

        // Delete value: "name"=-
        if value_part == "-" {
            unsafe {
                RegDeleteValueW(hkey, name_wide.as_ptr());
            }
            continue;
        }

        // DWORD value: "name"=dword:XXXXXXXX
        if let Some(hex_str) = value_part.strip_prefix("dword:") {
            if let Ok(dword_val) = u32::from_str_radix(hex_str, 16) {
                unsafe {
                    RegSetValueExW(
                        hkey,
                        name_wide.as_ptr(),
                        0,
                        REG_DWORD as u32,
                        &dword_val as *const u32 as *const u8,
                        4,
                    );
                }
            }
            continue;
        }

        // String value: "name"="value"
        if let Some(val) = parse_reg_string(value_part) {
            let val_wide: Vec<u16> = val.encode_utf16().chain(std::iter::once(0)).collect();
            unsafe {
                RegSetValueExW(
                    hkey,
                    name_wide.as_ptr(),
                    0,
                    REG_SZ as u32,
                    val_wide.as_ptr() as *const u8,
                    (val_wide.len() * 2) as u32,
                );
            }
            continue;
        }
    }

    if let Some(hk) = current_hkey {
        unsafe { RegCloseKey(hk) };
    }

    Ok(())
}

/// Parse a root key name and subkey path from a combined string like
/// `HKEY_LOCAL_MACHINE\Software\Something`.
#[cfg(windows)]
fn parse_root_and_subkey(
    path: &str,
) -> Option<(windows_sys::Win32::System::Registry::HKEY, &str)> {
    use windows_sys::Win32::System::Registry::{
        HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, HKEY_USERS,
    };

    let (root_name, subkey) = path.split_once('\\')?;
    let root = match root_name {
        "HKEY_LOCAL_MACHINE" => HKEY_LOCAL_MACHINE,
        "HKEY_CURRENT_USER" => HKEY_CURRENT_USER,
        "HKEY_CLASSES_ROOT" => HKEY_CLASSES_ROOT,
        "HKEY_USERS" => HKEY_USERS,
        _ => return None,
    };
    Some((root, subkey))
}

/// Delete an entire registry key tree.
#[cfg(windows)]
fn delete_key_tree(root: windows_sys::Win32::System::Registry::HKEY, subkey: &str) {
    use windows_sys::Win32::System::Registry::{
        RegCloseKey, RegDeleteTreeW, RegOpenKeyExW, KEY_WOW64_64KEY, KEY_WRITE,
    };

    if let Some((parent, leaf)) = subkey.rsplit_once('\\') {
        let parent_wide: Vec<u16> = parent.encode_utf16().chain(std::iter::once(0)).collect();
        let leaf_wide: Vec<u16> = leaf.encode_utf16().chain(std::iter::once(0)).collect();
        unsafe {
            let mut hkey = std::ptr::null_mut();
            let result =
                RegOpenKeyExW(root, parent_wide.as_ptr(), 0, KEY_WRITE | KEY_WOW64_64KEY, &mut hkey);
            if result == 0 {
                RegDeleteTreeW(hkey, leaf_wide.as_ptr());
                RegCloseKey(hkey);
            }
        }
    } else {
        let subkey_wide: Vec<u16> = subkey.encode_utf16().chain(std::iter::once(0)).collect();
        unsafe {
            RegDeleteTreeW(root, subkey_wide.as_ptr());
        }
    }
}

/// Parse a quoted string value: `"some value"` → `some value`.
/// Handles escaped backslashes (`\\` → `\`) inside the string.
#[cfg(windows)]
fn parse_reg_string(s: &str) -> Option<String> {
    let s = s.trim();
    if !s.starts_with('"') || !s.ends_with('"') || s.len() < 2 {
        return None;
    }
    let inner = &s[1..s.len() - 1];
    Some(inner.replace("\\\\", "\\"))
}

/// Parse `"name"=value` into `(name, value)`.
#[cfg(windows)]
fn parse_name_and_value(line: &str) -> Option<(String, &str)> {
    let rest = &line[1..]; // skip opening "
    let end_quote = rest.find('"')?;
    let name = &rest[..end_quote];
    let after_name = &rest[end_quote + 1..]; // skip closing "
    let value_part = after_name.strip_prefix('=')?;
    Some((name.to_string(), value_part))
}

#[cfg(not(windows))]
pub fn apply_registry(_entries: &[&str]) -> Result<(), InstallError> {
    Ok(())
}