#pragma once

#include <opencv2/core.hpp>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <optional>
#include <string>
#include <vector>

namespace target_exposure {

// All timestamps use caller-supplied, nonnegative microseconds in one clock domain.
using TimestampUs = std::int64_t;
enum class State { CAPTURE, TRACK, LOST };
enum class ResetReason { Startup, Manual, NewBusinessCycle, ClockChanged,
                         ConfigurationChanged, IdleTimeout, HistoryExpired };
enum class MeterStatus { Valid, NoTarget, EmptyImage, UnsupportedImage,
                         InvalidRoi, EmptyRoi, InsufficientPixels, InvalidConfiguration };
enum class PredictionReason { Available, Disabled, ModelNotConfirmed,
    CurrentMeasurementInvalid, InsufficientHistory, MissingHorizon,
    InvalidHorizon, DarkOrSaturated, ResidualTooLarge, OutOfRange, InvalidNumbers };
enum class Reason { Initialized, Ready, InvalidConfiguration, InvalidTimestamp,
    DuplicateFrame, OutOfOrderFrame, PreCaptureRequired, InvalidActualExposure,
    ConfirmingTarget, TrackingActivated, InvalidMetering, Deadband, Hysteresis,
    ConfirmingError, ProportionalAdjustment, PiAdjustment, ExposureLimit,
    TargetMissing, EnteredLost, Frozen, CaptureAfterFreeze, RecoveryNotAllowed,
    RecoveryReferenceMissing, RecoveryNotNeeded, RecoverySuggested, NotRecovered };

const char* toString(State value) noexcept;
const char* toString(ResetReason value) noexcept;
const char* toString(MeterStatus value) noexcept;
const char* toString(PredictionReason value) noexcept;
const char* toString(Reason value) noexcept;

struct MeteringConfig {
    double trim_fraction_each_side = 0.05;
    std::size_t min_target_pixels = 16;
    std::size_t min_retained_pixels = 8;
    // 1 = whole image; otherwise a fixed centered rectangle of this width/height fraction.
    double global_center_fraction = 1.0;
    int near_black_level = 2;
    int saturation_level = 253;
};
struct PredictionConfig {
    bool enabled = true;
    // Set only when gain/response and known black offset support the linear model.
    bool photometric_model_confirmed = false;
    std::size_t points = 3; // exactly 3 or 5, no implicit 5-to-3 fallback
    double black_level = 0.0;
    TimestampUs nominal_interval_us = 0; // 0 requires next_capture_timestamp_us
    TimestampUs max_horizon_us = 60'000'000;
    double max_relative_fit_rmse = 0.10;
    double max_near_black_fraction = 0.10;
    double max_saturated_fraction = 0.05;
    double min_predicted_gray = 1.0;
    double max_predicted_gray = 254.0;
};
struct ControllerConfig {
    double target_gray = 118.0;
    double deadband_ratio = 0.10;
    double hysteresis_ratio = 0.02;
    double large_error_ratio = 0.40;
    double proportional_gain = 0.70;
    double kp = 0.40;
    double ki = 0.10;
    double integral_abs_limit = 1.0;
    double max_step_ratio = 0.25; // applies to both proportional and PI branches
    int same_direction_frames = 2; // small error only, matching the approved pseudocode
};
struct RecoveryConfig {
    std::optional<double> global_reference_gray;
    double deadband_ratio = 0.30;
    double gain = 0.30;
    double max_step_ratio = 0.10;
};
struct Config {
    std::string profile_id = "default";
    std::uint64_t revision = 0;
    // Required from the caller. No motion-scene exposure maximum is hardcoded.
    double min_exposure_us = 0.0;
    double max_exposure_us = 0.0;
    double empirical_exposure_us = 0.0;
    TimestampUs history_window_us = 300'000'000;
    TimestampUs idle_timeout_us = 300'000'000;
    std::size_t history_capacity = 512;
    int detect_confirm_frames = 3;
    int lost_confirm_frames = 3;
    int freeze_frames = 2;
    MeteringConfig metering;
    PredictionConfig prediction;
    ControllerConfig controller;
    RecoveryConfig recovery;
};

std::vector<std::string> validate(const Config& config);
bool operator==(const Config& a, const Config& b);
inline bool operator!=(const Config& a, const Config& b) { return !(a == b); }

struct Roi {
    std::vector<cv::Rect> rectangles;
    std::vector<cv::RotatedRect> rotated_rectangles;
    // Each nonzero CV_8UC1 pixel is included. Full image dimensions are required.
    std::vector<cv::Mat> masks;
};
// Explicit helpers only; processFrame never calls these on the supplied final ROI.
cv::Rect inset(const cv::Rect& rectangle, double fraction_per_side);
cv::RotatedRect inset(const cv::RotatedRect& rectangle, double fraction_per_side);

struct Brightness {
    // Existing statistic: target trimmed mean; global untrimmed mean.
    std::optional<double> gray;
    MeterStatus status = MeterStatus::EmptyImage;
    std::size_t pixels = 0;
    std::size_t retained_pixels = 0;
    double near_black_fraction = 0.0;
    double saturated_fraction = 0.0;
    // Ordinary mean before trimming; absent whenever the measurement is invalid.
    std::optional<double> arithmetic_gray;
    bool valid() const noexcept { return status == MeterStatus::Valid && gray.has_value(); }
};
struct MeteringResult { Brightness target; Brightness global; };

// Stateless Gray8/BGR8 measurement. No exposure, timestamp or control instance needed.
// hasUsableRegion describes the supplied ROI, not confirmed physical target presence.
// Reads image/masks synchronously without retaining or changing them. Calls may run
// concurrently when the caller keeps the input image/mask data unchanged.
MeteringResult measureImage(const cv::Mat& image, const Roi& roi, bool hasUsableRegion,
                            const MeteringConfig& config = {});

struct HistoryRecord {
    TimestampUs timestamp_us = 0;
    double actual_exposure_us = 0.0;
    bool has_usable_target = false;
    MeteringResult metering;
    std::string profile_id;
    std::uint64_t config_revision = 0;
};
struct PredictionResult {
    PredictionReason reason = PredictionReason::InsufficientHistory;
    bool available = false;
    bool adopted = false;
    std::size_t points_used = 0;
    std::optional<TimestampUs> timestamp_us;
    std::optional<double> predicted_gray;
    std::optional<double> normalized_slope_per_second;
    std::optional<double> relative_fit_rmse;
};
struct ControlTrace {
    std::optional<double> current_error_ratio;
    std::optional<double> control_error_ratio;
    double integral = 0.0;
    int same_direction_count = 0;
    double raw_delta_exposure_us = 0.0;
    double limited_delta_exposure_us = 0.0;
    bool integral_blocked_by_limit = false;
    bool step_limited = false;
    bool exposure_limited = false;
};
struct FrameInput {
    cv::Mat image; // Gray8 or BGR8, read synchronously; no image retained after the call
    Roi roi;
    bool has_usable_target = false;
    TimestampUs timestamp_us = 0;
    double actual_exposure_us = 0.0; // finite and inside the configured limits
    std::optional<TimestampUs> next_capture_timestamp_us;
    bool allow_no_target_recovery = false;
};
struct PreCaptureResult {
    bool accepted = false;
    State state = State::CAPTURE;
    bool initialization_required = false;
    std::optional<double> suggested_exposure_us;
    Reason reason = Reason::PreCaptureRequired;
    std::optional<ResetReason> initialization_reason;
    std::vector<std::string> errors;
};
struct FrameResult {
    bool accepted = false;
    State state = State::CAPTURE;
    Reason reason = Reason::PreCaptureRequired;
    double actual_exposure_us = 0.0;
    bool adjustment_suggested = false;
    std::optional<double> suggested_exposure_us;
    MeteringResult metering;
    std::size_t valid_history_count = 0;
    PredictionResult prediction;
    ControlTrace control;
    int detection_count = 0;
    int loss_count = 0;
    int freeze_remaining = 0;
    bool loss_episode_active = false;
    bool recovery_used = false;
};

// One instance per independent camera/stream. Serialize calls to the same instance.
class ExposureControl {
public:
    ExposureControl();
    ~ExposureControl();
    ExposureControl(const ExposureControl&) = delete;
    ExposureControl& operator=(const ExposureControl&) = delete;
    PreCaptureResult preCapture(TimestampUs now_us, const Config& config);
    FrameResult processFrame(const FrameInput& input);
    // Only NewBusinessCycle opens a new recovery budget without stable detections.
    // ClockChanged also clears the timestamp watermark; it preserves the loss budget.
    void reset(ResetReason reason);
    State state() const noexcept;
    std::vector<HistoryRecord> history() const;
private:
    struct Impl;
    std::unique_ptr<Impl> impl_;
};

} // namespace target_exposure